I've recently started looking at the possibilities for a rubble trench foundation. Since it's a bank barn, I'll be backfilling on three sides, but the wall at the lower end of the slope will be exposed and therefore will be built from block or mortared stone. I haven't figured out how well that will integrate with the rubble trench on the other walls, though.

I'd hate to think about having to mix enough cement on site for full foundation walls. (No way to get a cement truck into the site.) I did look at some ICF options that would allow me to use less cement, but it still seemed way over-engineered for an unheated barn.